Contemporary torque motors may have a power density of 1 kW/kg. However, in all the technical fields in which such motors are used, efforts are also being made, inter alia, to improve this power density. This would be advantageous, in particular, in the automobile industry or aircraft industry. Specifically, in the aircraft industry, drive systems with a power density of 8 kW/kg are required.
Electric drive systems are currently generally used only for model aircraft. For example, a high-pole-number motor as an aircraft electric motor without a transmission is known from Geiger Engineering. The electric motor has a magnetic pole number of 42 and a power of 20 kW with a limiting rotational speed of 2500 revolutions per minute. For the starting phase, this motor has a power-to-weight ratio of 3.6 kW/kg.
In transverse flux machines, the magnetic flux runs transversely (e.g., perpendicularly) with respect to the rotational plane. In three-phase transverse flux machines, each phase may have its own excitation. However, transverse flux machines in which the three phases are fed by just one permanent magnet system are also known. Transverse flux machines are able to implement high pole pair numbers and therefore have small pole pitches. The iron weight per pole is therefore small, and consequently a favorable power-to-weight ratio is obtained. The winding heads are eliminated owing to the ring winding.
Document WO 2013/087412 A1 discloses a polyphase transverse flux machine in which Halbach arrays are arranged on the rotor. In order to form a closed magnetic flux, in addition, I cores are provided adjacent to corresponding yokes in the stator. As a result of the spatial proximity of the yokes to the I cores, the problem arises that an undesired transverse flux occurs which brings about magnetic saturation between the yokes and the I cores. This results in the torque yield remaining the same at high currents.